This application claims priority under 35 USC xc2xa7119 to Japanese Patent Application No. 2001-329476 filed on Oct. 26, 2001, the entire contents of which are hereby incorporated herein by reference.
1. Field of the Invention
This invention relates to a sheet feeding method and apparatus capable of supplying sheets, serving as recording mediums, either to an image forming device, arranged in a copier, a printer, a facsimile, a complex machine combining these functions, or the like, or a printing device arranged in a printer.
2. Discussion of the Background
In an image forming apparatus typified by a copier or printer, an image is generally formed on a recording medium, such as a sheet, an OHP sheet, etc. (hereinafter simply referred to as a sheet), in accordance with read or input image information. When the image is formed, sheets should be fed toward an image forming section one by one. The plural sheets are generally stacked on a sheet feeding tray or cassette, and are separated and withdrawn from the upper most sheet one by one, thereby being launched from the stack toward the image forming section. Such a mechanism is generally referred to as a xe2x80x9csheet separating mechanismxe2x80x9d as illustrated in FIG. 7 as one example.
FIG. 7 roughly illustrates a background sheet separating mechanism that picks up the upper most sheet S1 from among a sheet bundle stacked on a sheet-feeding tray 1. Also roughly illustrated is a route that conducts a sheet to a transfer position of a photoconductive member 7 from the sheet separating mechanism by a pair of register rollers 4. The sheet separating mechanism is configured from a sheet-feeding roller 2, a separating pad 3, and a pressure spring 3a that biases the separating pad 3 toward the sheet-feeding roller 2.
The sheet bundle loaded on the sheet feeding tray 1 is pushed up by an elevation mechanism (not shown) so that the upper most sheet S1 can pressure contact the sheet feeding roller 2 arranged in the sheet exit side of the sheet feeding tray 1. The separation pad 3 is provided biased by the pressure spring 3a and is arranged to oppose the sheet feeding roller 2. Thus, the separation pad 3 is elastically biased and pushed toward the sheet-feeding roller 2 by the pressure spring 3a. 
In such a condition, when the sheet feeding roller 2 is rotated upon reception of a sheet feeding signal from a control section (not shown) of an image forming apparatus, only the uppermost sheet S1 is separated and fed toward the following register roller 4. The register roller 4 of this embodiment is arranged substantially perpendicular to and above the sheet-feeding tray 1. Thus, a sheet S is upwardly fed along a guide plate 5. Then, the tip of a sheet S arrives at a nip of the pair of the register rollers 4, and a sheet S slackens and enters a standby state to synchronize with a tip of a visualized image developed by toner on the photoconductive (PC) member 7. Further, reference numeral 6 represents a transfer roller. Various known apparatuses of charging, writing, charge removing, developing, transferring, separating, and cleaning apparatuses and so on are arranged to execute a conventional electronic photographic process along the outer circumference of the PC member 7.
Thus, both the register roller 4 and sheet-feeding roller 2 recommence to drive in synchronism with the tip of the visualized image. A sheet S is lead to the nip formed between the PC member 7 and the transfer roller 6. After receiving transfer of a toner image, the sheet S is separated from the PC member 7 by a separating apparatus (not shown). The sheet S is then ejected from a sheet ejection section after the visualized image is fixed by a fixing apparatus (not shown).
Further, a sheet feeding speed on a path downstream of the sheet feeding roller 2 to a position immediately before the pair of register rollers 4 is set to be faster than that on a path downstream of the register roller pair 4, i.e., from register roller pair 4 to the sheet ejection section by the PC member 7 and the fixing section. That is, the sheet feeding speed is increased until a position immediately before the register roller pair 4 to shorten a first printing time period.
As shown in FIG. 8, in such a sheet separation mechanism, the uppermost sheet S2 of the next job is not fed (i.e., the tip S2h of the sheet S2 stops at an entrance of the separation pad 3) when the register roller 4 and sheet feeding roller 2 resume driving so that a sheet S1 corresponding to the last copy of a job can synchronize with a tip of the above-described visualized image. As a result, when the trailing end S1e of the sheet S1 exits from the nip formed between the sheet feeding roller 2 and separation pad 3, the separation pad 3 is flipped by the trailing end S1e of the sheet S1 and hits the sheet feeding roller 2 or is pulled in a sheet S feeding direction and is flipped by the pressure spring 3a and contacts the surfaces of the sheet feeding tray 1 guide and sheet feeding roller 2. As a result, percussive noises are occasionally created. Further, the noise can be amplified by resonance of the pressure spring 3a. 
Accordingly, an object of the present invention is to address and resolve the above-noted and other problems and provide a novel sheet feeding apparatus and method that address and resolve the above-noted and other problems.
The above and other objects are achieved according to the present invention by providing a novel sheet feeding apparatus and method including launching sheets stacked on a sheet feeding tray using a sheet feeding roller, separating double feed sheets using a separation pad, and feeding a separated sheet to a prescribed position. Further, the separated sheet is controlled to always intervene between the sheet feeding roller and separation pad when the sheet feeding roller stops rotating.
In another embodiment, a job is completed by stopping feeding of a sheet when a last sheet of the job is completed, and when a headmost sheet of the next job is continuously fed and pinched by the sheet feeding roller and separation pad.
In yet another embodiment, a sheet feeding apparatus includes a sheet feeding tray configured to stack and maintain sheets, a sheet feeding roller operative to launch the sheets stacked on the sheet feeding tray, and a separation pad operative to separate launched sheets when double feed occurs. Further, the sheet feeding roller stops rotating while pinching a headmost sheet of the next job in cooperation with the separation pad after the last sheet of a precedent job is fed.
In yet another embodiment, an inertia-generating device is provided in a sheet feed driving unit to generate inertia force, and the inertia-generating device controls the stoppage of the sheet-feeding roller.
In yet another embodiment, the inertia-generating device includes a flywheel.
In yet another embodiment, the controlling device, which adjusts a timing of canceling power transmission of a power transmitting mechanism, controls the sheet-feeding roller to stop.